(1) Field of the Invention
This invention pertains generally to fluid temperature transducers, and is more particularly concerned with transducers utilized for limiting the temperature of a fluid flowing through a duct.
(2) Description of the Prior Art
Typical of the prior art is a transducer arrangement employing a bimetallic disc supported at its edge and having a needle valve extending from a plug secured at the center of the disc. A needle valve is cooperatively disposed vis-a-vis a vent orifice formed in the housing and communicating with a source of fluid whose pressure is to be controlled by the positioning of the needle valve in accordance with the temperature of a sensed fluid in contact with one face of the bimetallic disc.
In order to minimize (to the extent possible) the effect of the pressure of the sensed fluid on the bimetallic disc, the disc is mounted in a cup-like container so that the bimetallic disc senses fluid temperature in the space defined by the disc and the container. The cup-like container is provided with a small bleed aperture which permits a bleed of the sensed fluid to flow across one face of the bimetallic disc and thereafter be vented. The claim is made that the bleed aperture is so small as to have little, if any, effect upon the pressure of the sensed fluid.
It will be noted that the bimetallic disc and needle valve assembly requires a shroud to shield the other face of the bimetallic disc against the influence of the temperature of the fluid vented by the needle valve.
It will be obvious to those skilled in the art that such a transducer is unnecessarily complex, lacking in rapid and accurate response to the temperature of the sensed fluid, and is comprised of a multiplicity of parts which tends to degrade the reliability of the device.
It was considered that transducers of the prior art, such as that briefly mentioned above, could be materially improved if the pressurized fluid to be controlled was caused to flow through a passageway having a poppet valve and valve seat means spaced from and disassociated from the general location of the bimetallic disc and the fluid sensed by it. The novel concept was that the poppet valve would have a stem of small section, extending through a guide bore in the main housing member, with the distal end of the stem projecting toward the center of a bimetallic disc secured at its peripheral edge in an open cage-like housing member disposed in the stream of fluid whose temperature was to be sensed by the disc.
It was contemplated in the concept that the cage-like housing member would be threadably coupled to the main housing member with the disc spaced from and coaxially disposed relative to the valve stem so that the crack point temperature, at which the disc would contact the distal stem end, could be adjusted. With an arrangement of this type the fluid whose temperature was to be sensed by the bimetallic disc would have free flow contact with both faces of the disc without materially disturbing or impeding the flow of the sensed fluid. Hence the disc could provide rapid response to temperature changes of the sensed fluid with excellent accuracy since there would be no heat transfer from the sensed fluid to the ambient through a complicated array of mechanical components disposed in the sensed fluid flow path.
A natural consequence of this novel concept was a reduction in the number of parts (and hence of maintenance requirements) with a concomitant increase of reliability. The present invention was conceived on this novel concept.